(a) Field of the Invention
The present invention relates to a microscope objective and, more particularly, to a plan achromat class microscope objective with a medium class magnification of which the working distance is very long and aberrations are corrected favourably up to the marginal portion of field.
(b) Description of the Prior Art
Among known microscope objectives, the microscope objective disclosed in Japanese published unexamined patent application No. 128154/77, for example, is known as a microscope objective with a long working distance and NA about 0.4. However, most of such known microscope objectives do not have satisfactorily long working distance. On the other hand, there is a demand for a microscope objective with a long working distance from the view point of convenience in use.
Besides, regarding the microscope objective, there is such tendency that aberrations are aggravated sharply when the working distance is made long by keepting the same degree of NA and, as a result, it becomes difficult to obtain favourable quality of image.